1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device capable of receiving touch commands.
2. Description of the Prior Art
With rapid development in technology, massive amount of data can be transmitted, processed and stored in digital formats. Electronic devices capable of accessing digital data have thus become important tools in modern society. Notebook computers, mobile phones, and personal digital assistants (PDAs) are light and easy-to-carry portable electronic devices that allow users to search, read and store different types of digital data. Since portable electronic devices aim at light weight and thin appearance, there is usually insufficient space for traditional input devices such as keyboard or mouse. Instead, touch panels are commonly used for portable electronic devices as the human-machine interface for data transmission. When a user enters a touch command by pressing a touch panel, the touch panel can detect the location of the applied pressure (or the amount of the applied pressure) and control the operation of the portable device accordingly.
Liquid crystal display (LCD) panels are commonly used for display screens in portable electronic devices. Based on how input commands are identified, touch panels can be categorized into four major types: resistive, capacitive, surface wave and optical touch panels. Reference is made to FIG. 1 for a diagram of a prior art LCD device 10. The LCD device 10 includes an LCD panel 110 and a resistive touch panel 120. The resistive touch panel 120 and the LCD panel 110 are connected via an adhesion glue film 140. The LCD panel 110 includes a first substrate 112, a first electrode 114, a liquid crystal layer 115, a second electrode 116, and a second substrate 118. The resistive touch panel 120 includes a substrate 122, a lower transparent conducting film 124, a plurality of dot spacers 125, an upper transparent conducting film 126, a connecting layer 127, a polyethylene terephthalate (PET) layer 128, and a trace 130. The connecting layer 127 is disposed between the upper transparent conducting film 126 and the lower transparent conducting film 124, and the dot spacers 125 are disposed in a matrix manner within the space between the upper transparent conducting film 126 and the lower transparent conducting film 124. When a user applies a pressure on the PET layer 128 using a finger, a pen or other input devices, the upper transparent conducting film 126 and the lower transparent conducting film 124 will make contact with each other at the exact point of the applied pressure, thereby generating a corresponding voltage. The voltage is then transmitted to a central processor (not shown in FIG. 1) via the trace 130 for identifying the touch command entered by the user. Since the resistive touch panel 120 and the LCD panel 110 are connected via the adhesion glue film 140, the prior art LCD device 10 required many stacks of different layers, resulting in higher manufacturing costs, larger size and heavier weight. Optical performances such as brightness or contrast of the prior art LCD device 10 will also be influenced.
Reference is made to FIG. 2 for a diagram of an LCD device 20 disclosed in U.S. Patent Publication No. US2006/0017710. The LCD device 20 includes a plurality of data lines, a plurality of gate lines, a plurality of sensor signal lines, and a plurality of pixels. For ease of explanation, only a data line DL, a gate line GL, sensor signal lines Pj, Si, Psd, and a pixel PX are illustrated in FIG. 2. The pixel PX includes a display unit DC and a detecting unit DC. The display unit DC, coupled to the data line DL and the gate line GL, includes a thin film transistor (TFT) switch TFT1, a liquid crystal capacitor CLC and a storage capacitor CST. The detecting unit SC, coupled to the sensor signal lines Pj, Si and Psd, includes a thin film transistor switch TFT2, a thin film transistor switch TFT3, and a variable capacitor CV. In the LCD device 20, when a user enters a touch command, the applied force changes the capacitance of the variable capacitor CV, thereby changing the gate voltage of the thin film transistor TFT3. After the thin film transistor TFT3 is turned on, signals corresponding to trails of the touch command can be transmitted to a central processor (not shown in FIG. 2) via the turned-on thin film transistor TFT3 and the sensor signal line Psd for identifying the touch command. In the prior art LCD device 20, the capacitance of the variable capacitor CV depends on the amount of force from the user when entering the touch command. Since the gate voltage of the thin film transistor TFT3 cannot be controlled directly, residual charges may blur the signals corresponding to the touch command, and the ability to identify different touch commands accurately is thus influenced.
Reference is made to FIG. 3 for a diagram of an LCD device 30 disclosed in U.S. Patent Publication No. US2004/0169625. The LCD device 30 includes a first substrate 112, a first electrode 114, a liquid crystal layer 115, a second electrode 116, and a second substrate 118. The second electrode 116 is disposed on the second substrate 118 and includes a plurality of pixels PX. A plurality of photo diodes PD are also disposed on the second substrate 118 for sensing input signals given by a user using a light source 150 (such as an optical pen). Optical signals detected by the photo diodes PD can then be transmitted to a central processor (not shown in FIG. 3) for identifying commands given by the user using the light source 150. The prior art LCD device 30 can detect input signals from external light source using the photo diodes PD, but is unable to identify input signals corresponding to touch commands.